Japanese Unexamined Patent Publication No. 2013-197183 discloses a semiconductor manufacturing system. The semiconductor manufacturing system includes a processing container (chamber) and a diffusion chamber which is disposed inside the processing container and communicates with the processing container. The system supplies a first gas and a second gas from gas supply sources into the processing container through the diffusion chamber, and repeatedly performs an etching process and a deposition process which plasma-process a silicon substrate. In the semiconductor manufacturing system, at timing when the etching process and the deposition process are switched, while a remaining gas of a previous process in the diffusion chamber is exhausted, a gas of the next process is introduced into the diffusion chamber, and opening and closing of a valve causes the gas of the next process to rapidly flow into the diffusion chamber. Accordingly, remaining of the gas of the previous process is prevented, and a time in which the gases between processes are switched is shortened.